Week -2
1.Aim: To build Simulink model of Doorbell using solenoid block.
Objective: when the switch is closed the electromagnet receives electrical power from the battery and pulls the metal arm to hit the bell producing sound. Create a situation where the switch is closed for 2 seconds and then released. Observe the physical movement of the plunger.
Solenoid: A solenoid is a device comprised of a coil of wire, the housing and a moveable plunger (metal arm). When an electrical current is introduced, a magnetic field forms around the coil which draws the plunger in. More simply, a solenoid converts electrical energy into mechanical work.
Door Bell:A doorbell is a signaling device typically placed near a door to a building's entrance. When a visitor presses a button the bell rings inside the building, alerting the occupant to the presence of the visitor. Although the first doorbells were mechanical, activated by pulling a cord connected to a bell, modern doorbells are electric, operated by a pushbutton switch. Modern doorbells often incorporate intercoms and miniature video cameras to increase security.
But In this challange we will implement door bell using solenoid blocks only.
Working principle of Doorbell Using Solenoid:
Fig(1) Electric Door Bell
When the switch is on the current flows through the electromagnet(solenoid) which produces the magnetic field and attracts the clapper. The clapper strikes the bell which produces the noise and once the clapper strikes electrical contact is broken and no current flows through it. Therefore the clapper will come back because of no magnetic field and again the circuit is closed and again the striker strikes the bell. This process will repeats until when the switch is off.
Simulink model:
Fig(2). Simulink model of Door Bell using Solenoid.
1. The blocks used in simulation are:
(a) Pulse generator.
(b) switch.
(c) Battery.
(d) solenoid.
(e) motion sensor.
(f) solver configaration.
(g) simulink to ps converter and ps to simulink converter.
(h) scope and display.
2. Here the main important tools are switch and solenoid. for the switch battery will be given to the power supply and also pulse generator is connected to control it. The pulse generator phase dealy is chosen as 2sec as per the objective shown in figure 3. From this we should understand that when the pulse is given then only the switch is turned on other wise it is turned off.
3. The solenoids are of two types
(a)port R moves away from port c.
(b) port R moves towards port c.
Where R is plunger and C is a Case.
4. The ideal motional sensor is nothing but clapper shown in figure (1). From this sensor the output scope is connected.
Fig(3). Pulse Generator
5. Solver configaration is used to run the simulation of the circuit and it is connected to the common point C of solenoid and motion sensor.
Results: The following waveforms are obtained when the battery voltage is 12V only and phase delay is 2sec and assume intial position of motion sensor is zero. The solenoid parameters are shown in fig.4
Fig(4) solenoid Parameters
Output of motion sensor when the solenoid of port R moves away from port c:
Fig(5). Output of motion sensor when the solenoid of port R moves away from port c.
Output of motion sensor when the solenoid of port R moves towards port c:
Fig(6). Output of motion sensor when the solenoid of port R moves towards port c.
From the fig. 5 it is observed that the first half cycle is positive where as fig.6 the first half cylce is negative.
Case i:Now we will see what will happens if motion sensor position is changed from zero to 1 and spring constant from 200 to 10, damping from 1 to 0.1 and constant damping from 500 to1. Here the solenoid is considered as port R moves towards port c.
Fig(7) Modified solenoid Parameters
Output of motion sensor when the solenoid of port R moves towards port c:
Fig(8). Output of motion sensor when the solenoid of port R moves towards port c when spring constant is 10, damping is 0.1 and constant damping is 1
case 2: Here only damping is changed from 0.1 to 1 and remaining parameters are constant.
Fig.(9) Modified solenoid parameters.
Fig(10). Output of motion sensor when the solenoid of port R moves towards port c when spring constant is 10, damping is 1 and constant damping is 1 .
case3: Here spring constant is chosen as 2 and remaining parameters are same as that of previous case.
Fig.(10) Modified solenoid parameters.
Fig(11). Output of motion sensor when the solenoid of port R moves towards port c when spring constant is 2, damping is 1 and constant damping is 1.
From the Fig(8) it is observed that oscillations are very high due to less damping(0.1), low spring constant(10) , From the Fig(10) it it observed that no oscillations but only small spike because of higher damping constant(1), low spring constant(10) and From the Fig(11) it is observed that no oscillations because of higher damping constant(1) and lower spring constat(2).
2.Aim: Use a thermistor to sense the temperature of a heater & turn on or turn off the fan.
Objective: Temperature source: 20 °C from 0 to 10 seconds,
27 °C from 10 to 30 seconds,
23 °C from 30 to 50 seconds
Fan conditions: ON if the temperature above 25 °C OFF otherwise.
Thermistor: A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass.
Simulink Model:
Fig.(12) simulink diagram of thermistor to sense the temperature to turn on or off the fan.
1. The blocks used in the simulation are:
(a) Signal builder.
(b) Controlled temperature source.
(c) Thermistor.
(d) Voltage sensor.
(e) switch.
(f) Battery.
(g) scope.
(h) solver configaration and thermal reference.
2. The signal builder is connected to simulink to ps converter to the controlled temperature source which sets the temperature to the port A of the thermistor.
3. The battery positive terminal is connected to the negative terminal of the thermistor and the negative terminal of the battery is connected to the one of the terminal of the resistor and the other terminal of the resistor is connected to the positive terminal of the thermistor.
4. The voltage sensor output v is connected to the second terminal of the switch and also to the scope and display.
5. The first and third terminals are connected with some constants 1 and 0.
6. Based on the threshold value it will sets the output which is connected to the scope.
7. Based on the objective the signal builder will be arranged.
Temperature source: 20 °C from 0 to 10 seconds,
27 °C from 10 to 30 seconds,
23 °C from 30 to 50 seconds
Fan conditions: ON if the temperature above 25 °C OFF otherwise.
we know that 1°C =273.15K.
20°C--->From 0 to 10sec=293.15K.
27°C --->From 10 to 30sec=300.15.
23°C --->From 30 to 50sec=297.15.
Fig.(13) signal builder.
Fig.(14) Voltage Across the Resistor.
From the above figure it is clear that the output signal must be 1 when the temperature is greater than 25. There fore the threshold value is greater than 0.011 to get fan ON. Hence the threshold value is choosen as 0.011055 approximately.
Fig.(15) Switch threhold value.
Output:
Fig .(16) Output signal to fan
From the above figure it is concluded that from 0 to 10 the output signal is 0 because the magnitude of voltage across is less than threshold value, From 10 to 30 the signal is 1 because the magnitude of voltage across is greater than threshold value and from 30 to 50 the signal is 0 because the magnitude of voltage across is less than threshold value. This is analysis is valid only when the battery voltage is 12V.
The fan will ON only in between 10 to 30 sec ,from 0 to 10sec and 10 to 30sec Fan will OFF.
If the battery voltage is changed then obviously the threshold value of the switch must be changed. Let us assume the battery voltage is 24V then if the threshold value is same as that of previous value then the voltage across resistor and output signal as shown in below figures
Fig.(17) Voltage Across the Resistor.
Fig.(18) Output signal to fan.
To get the required output as per the objective the thershold value must be change. from the Fig 17 it is decided that threshold value is greater than 0.022. There fore for better result 0.0222 is choosen to meet the objective.
Fig.(19) Modified Switch threhold value.
After keeping the threshold value the output signal is shown in below fig(20).
Fig.(20) Output signal to fan.
For these case we have choosen that resistance value is 1. But if the resistance value is changes then obviously there is a change in threshold value discussed above.